Basically, it seems that the rMini use to type of screens:
Sharp: most (if not all) have some image retension, hardly visible in real life use, and otherwise very even backlight and colors. Colors are also more "vibrant" (close to the one of the iPad 3 or 4).
LG: suffer from the "yellowing", "blueish", and uneven color problem. Very variable from one rMini to another... Colors are a little more "muted".
Just my two cents...
If this is true, then I must have a screen made by Sharp. The display is bright and uniform with no yellowed areas. The colors are almost as vibrant as those on my iPhone 5. Haven't done an image retention test, as I haven't noticed any of that in normal usage.